#include<stdio.h>
int main()
{
    char an[]={'A','B','C','D'};
    char ans;
    int count=0;
    for(int i=0;i<4;i++)
    {
        count=0;
        ans=an[i];
 if(ans!='A')
    {
     count++;
    }
    if(ans=='C')
    {
        count++;
    }
    if(ans=='D')
    {
        count++;
    }
    if(ans!='D')
    {
        count++;
    }
    if(count==3)
    {
        printf("%c",ans);
    }
    }
   
    return 0;
}